Is the renal kallikrein-kinin system a factor that modulates calciuria? / ¿Es el sistema calicreína/quinina renal un factor modulador de la calciuria?

Renal tubular calcium reabsorption is one of the principal factors that determine serum calcium concentration and calcium excretion. Calcium excretion is regulated by the distal convoluted tubule and connecting tubule, where the epithelial calcium channel TRPV5 can be found, which limits the rate of transcellular calcium transport. The dynamic presence of the TRPV5 channel on the surface of the tubular cell is mediated by an endosomal recycling process. Different intrarenal factors are involved in calcium channel fixation in the apical membrane, including the anti-ageing hormone klotho and tissue kallikrein (TK). Both proteins are synthesised in the distal tubule and secreted in the tubular fluid. TK stimulates active calcium reabsorption through the bradykinin receptor B2 that compromises TRPV5 activation through the protein kinase C pathway. TK-deficient mice show hypercalciuria of renal origin comparable to that seen in TRPV5 knockout mice. There is a polymorphism with loss of function of the human TK gene R53H (allele H) that causes a marked decrease in enzymatic activity. The presence of the allele H seems to be common at least in the Japanese population (24%). These individuals have a tendency to greater calcium and sodium excretion in urine that is more evident during furosemide infusion. Future studies should analyse if manipulating the renal kallikrein-kinin system can correct idiopathic hypercalciuria with drugs other than thiazide diuretics.

Tissue kallikrein is required for the cardioprotective effect of cyclosporin A in myocardial ischemia in the mouse.

Clinical and experimental studies suggest that pharmacological postconditioning with Cyclosporin A (CsA) reduces infarct size in cardiac ischemia and reperfusion. CsA interacts with Cyclophilin D (CypD) preventing opening of the mitochondrial permeability transition pore (mPTP). Tissue kallikrein (TK) and its products kinins are involved in cardioprotection in ischemia. CypD knockout mice are resistant to the cardioprotective effects of both CsA and kinins suggesting common mechanisms of action. Using TK gene knockout mice, we investigated whether the kallikrein-kinin system is involved in the cardioprotective effect of CsA. Homozygote and heterozygote TK deficient mice (TK(-/-), TK(+/-)) and wild type littermates (TK(+/+)) were subjected to cardiac ischemia-reperfusion with and without CsA postconditioning. CsA reduced infarct size in TK(+/+) mice but had no effect in TK(+/-) and TK(-/-) mice. Cardiac mitochondria isolated from TK(-/-) mice had indistinguishable basal oxidative phosphorylation and calcium retention capacity compared to TK(+/+) mice but were resistant to CsA inhibition of mPTP opening. TK activity was documented in mouse heart and rat cardiomyoblasts mitochondria. By proximity ligation assay TK was found in close proximity to the mitochondrial membrane proteins VDAC and Tom22, and CypD. Thus, partial or total deficiency in TK induces resistance to the infarct size reducing effect of CsA in cardiac ischemia in mice, suggesting that TK level is a critical factor for cardioprotection by CsA. TK is required for the mitochondrial action of CsA and may interact with CypD. Genetic variability in TK activity has been documented in man and may influence the cardioprotective effect of CsA.

Partial genetic deficiency in tissue kallikrein impairs adaptation to high potassium intake in humans.

Inactivation of the tissue kallikrein gene in mice impairs renal handling of potassium due to enhanced H, K-ATPase activity, and induces hyperkalemia. We investigated whether the R53H loss-of-function polymorphism of the human tissue kallikrein gene affects renal potassium handling. In a crossover study, 30 R53R homozygous and 10 R53H heterozygous healthy males were randomly assigned to a low-sodium/high-potassium or a high-sodium/low-potassium diet to modulate tissue kallikrein synthesis. On the seventh day of each diet, participants were studied before and during a 2-h infusion of furosemide to stimulate distal potassium secretion. Urinary kallikrein activity was significantly lower in R53H than in R53R subjects on the low-sodium/high-potassium diet and was similarly reduced in both genotypes on high-sodium/low-potassium. Plasma potassium and renal potassium reabsorption were similar in both genotypes on an ad libitum sodium/potassium diet or after 7 days of a high-sodium/low-potassium diet. However, the median plasma potassium was significantly higher after 7 days of low-sodium/high-potassium diet in R53H than in R53R individuals. Urine potassium excretion and plasma aldosterone concentrations were similar. On the low-sodium/high-potassium diet, furosemide-induced decrease in plasma potassium was significantly larger in R53H than in R53R subjects. Thus, impaired tissue kallikrein stimulation by a low-sodium/high-potassium diet in R53H subjects with partial tissue kallikrein deficiency highlights an inappropriate renal adaptation to potassium load, consistent with experimental data in mice.

Tissue kallikrein, blood pressure regulation, and hypertension: insight from genetic kallikrein deficiency.

Tissue kallikrein has been suggested to be involved in blood pressure regulation and in protection against hypertension. However, this hypothesis remains debated. Recently, murine genetic models of kallikrein deficiency have been engineered and partial genetic deficiency in kallikrein activity has been characterized in humans. Studies in kallikrein-deficient mice indicate that kallikrein indeed influences blood pressure in the setting of mineralocorticoid excess and salt retention but not in normotensive animals and in high renin hypertension. These observations suggest that kallikrein can have antihypertensive function in physiological situations where sodium retention can trigger blood pressure elevation.

Kallikrein protects against microalbuminuria in experimental type I diabetes.

Tissue kallikrein is the main kinin-forming enzyme in mammals, and differences in kinin levels are thought to be a contributing factor to diabetic nephropathy. Here, we determined the role of the kallikrein-kinin system in the pathogenesis of streptozotocin-induced diabetic nephropathy in wild-type and tissue kallikrein-knockout mice. All diabetic mice developed similar hyperglycemia, but the knockout mice had a significant two-fold increase in albuminuria compared to the wild-type mice before and after blood pressure elevation. Ezrin mRNA, a podocyte protein potentially implicated in albuminuria, was downregulated in the kidney of knockout mice. One month after induction of diabetes, the mRNAs of kininogen, tissue kallikrein, kinin B1, and B2 receptors were all increased up to two-fold in the kidney in both genotypes. Diabetes caused a 50% decrease in renal angiotensin-converting enzyme expression and a 20-fold increase in kidney injury molecule-1 reflecting tubular dysfunction, but there was no genotype difference. Our study found an early activation of the kallikrein-kinin system in the kidney and that this has a protective role against the development of diabetic nephropathy. The effect of tissue kallikrein deficiency on microalbuminuria in diabetic mice is similar to the effect of genetically high angiotensin-converting enzyme levels, suggesting that both observations, in part, result from a deficiency in kinins.

Genetic deficiency in tissue kallikrein activity in mouse and man: effect on arteries, heart and kidney.

Tissue kallikrein (KLK1) is a kinin-forming serine protease synthesized in many organs including arteries and kidney. Study of the physiological role of KLK1 has benefited from the availability of mouse and human genetic models of KLK1 deficiency, through engineering of KLK1 mouse mutants and discovery of a major polymorphism in the human KLK1 gene that induces a loss of enzyme activity. Studies in KLK1-deficient mice and human subjects partially deficient in KLK1 have documented its critical role in arterial function in both species. KLK1 is also involved in the control of ionic transport in the renal tubule, an action that may not be kinin-mediated. Studies of experimental diseases in KLK1-deficient mice have revealed cardio- and nephro-protective effects of KLK1 and kinins in acute cardiac ischemia, post-ischemic heart failure, and diabetes. Potential clinical and therapeutic developments are discussed.

Tissue kallikrein deficiency aggravates cardiac remodelling and decreases survival after myocardial infarction in mice.

BACKGROUND: Tissue kallikrein (TK) is a major kinin-releasing enzyme present in arteries. TK is involved in cardioprotection in the setting of acute myocardial ischaemia but its role in post-ischaemic heart failure (HF), a major cause of delayed mortality after myocardial infarction (MI), is unknown. AIM: To determine whether TK deficiency in the mouse influences survival and cardiac remodelling after MI. METHODS: MI was induced in 10 week-old male TK-deficient mice and wild-type littermates. Survival was assessed up to 14 months. Cardiac morphological and functional parameters were serially measured by echocardiography. In another experiment, myocardial capillary density and NOS content were evaluated at 3 months. RESULTS: Infarct size was similar in both genotypes. MI resulted in severe cardiac dysfunction. Up to 12 months after MI, TK(-/-) mice displayed an increased mortality rate (P<0.05, relative risk of death=3.41) and aggravation of left ventricular hypertrophy and dilatation by comparison with TK(+/+) (+18% and +27% respectively, both P<0.05). NOS1 and NOS3 were abnormally regulated in the heart of TK(-/-) mice after MI. CONCLUSIONS: TK exerts a protective role in HF in mice. Coronary effects are probably involved. As partial genetic deficiency in TK activity occurs in humans, TK-deficient subjects may be at increased risk of mortality in HF.

Tissue kallikrein-deficient mice display a defect in renal tubular calcium absorption.

Renal tubular calcium (RTCa) transport is one of the main factors that determine serum Ca concentration and urinary Ca excretion. The distal convoluted and connecting tubules reabsorb a significant fraction (10%) of filtered Ca. These tubule segments also synthesize in large abundance tissue kallikrein (TK), a major kinin-forming enzyme. Tested was the hypothesis that TK and kinins are involved in controlling RTCa transport by studying TK (TK-/-) or kinin B2 receptor (B2-/-)-deficient mice on different Ca diets. On a 0.9% wt/wt Ca diet, 129Sv or C57Bl/6 TK-/- mice excreted significantly more Ca in urine than their wild-type (WT) littermates. There was no difference between TK-/- and WT mice for plasma concentrations of Ca, Mg, creatinine, parathyroid hormone, or 1,25-dihydroxyvitamin D. On a low Ca (LCa) diet (0.01% wt/wt), urinary Ca excretion decreased in both TK-/- and WT mice but still remained higher in TK-/- mice compared with WT. The plasma Ca concentration was unchanged in C57Bl/6 TK-/- mice but decreased significantly in 129Sv TK-/- mice. Taken together, these data demonstrate that TK deficiency led to impaired RTCa absorption. On the LCa diet, renal TK gene expression doubled in WT mice. No change in urinary Ca excretion was observed in B2-/- mice, even after treatment with a kinin B1-receptor antagonist, and these mice adapted normally to the LCa diet. TK deficiency had no effect on the renal abundance of distal Ca transporter mRNA. These data suggest that TK may be a physiologic regulator of RTCa transport, acting through a non-kinin-mediated mechanism.

Flow-dependent dilation mediated by endogenous kinins requires angiotensin AT2 receptors.

The vascular kallikrein-kinin system contributes to about one third of flow-dependent dilation in mice carotid arteries, by activating bradykinin B2 receptors coupled to endothelial nitric oxide (NO) release. Because the bradykinin/NO pathway may mediate some of the effects of angiotensin II AT2 receptors, we examined the possible contribution of AT2 receptors to the kinin-dependent response to flow. Changes in outer diameter after increases in flow rate were evaluated in perfused arteries from wild-type animals (TK+/+) and in tissue kallikrein-deficient mice (TK-/-) in which the presence of AT2 receptor expression was verified. Saralasin, a nonselective angiotensin II receptor antagonist, impaired significantly flow-induced dilation in TK+/+, whereas it had no effect in TK-/- mice. In both groups, blockade of AT1 receptors with losartan or candesartan did not affect the response to flow. Inhibition of AT2 receptors with PD123319 reduced significantly flow-induced dilation in TK+/+ mice, but had no significant effect in TK-/- mice. Combining PD123319 with the bradykinin B2 receptor antagonist HOE-140 had no additional effect to AT2 receptor blockade alone in TK+/+ arteries. Flow-dependent-dilation was also impaired in AT2 receptor deficient mice (AT2-/-) when compared with wild-type littermates. Furthermore, HOE-140 significantly reduced the response to flow in the AT2+/+, but not in AT2-/- mice. In conclusion, this study demonstrates that the presence of functional AT2 receptors is necessary to observe the contribution of the vascular kinin-kallikrein system to flow-dependent dilation.

Uterine artery structural and functional changes during pregnancy in tissue kallikrein-deficient mice.

OBJECTIVE: Tissue kallikrein (TK) participates in acute flow-induced dilatation (FID) of large arteries. We investigated whether TK deficiency blunts FID and alters chronic flow-related arterial structural and functional changes in resistance-sized muscular arteries. METHODS AND RESULTS: Vasomotor responses and structural parameters were determined in uterine arteries isolated from nonpregnant, 18- to 19-day pregnant, and 7-day postpartum TK-/- and TK+/+ littermate mice. In TK-/- mice, values of diameter, medial cross-sectional area (CSA), myogenic tone, and dilatation in response to acetylcholine were comparable to those values in TK+/+ mice, but FID (0 to 100 microL/min) was significantly reduced (55+/-4% versus 85+/-4% in TK+/+ mice). In both mouse strains, pregnancy resulted in significant increases in diameter and medial CSA and in the Nw-nitro-l-arginine methyl ester-sensitive component of FID. By 7 days after pregnancy, uterine arterial diameter and CSA values no longer differed from nonpregnant values, and FID was markedly reduced in TK-/- and TK+/+ mice. CONCLUSIONS: These observations (1) confirm at the level of resistance arteries the key role of TK in FID and (2) indicate that TK deficiency does not compromise arterial remodeling and changes in the contribution of NO to FID during and after pregnancy.